What is a CLSID?A Class ID (CLSID) is a 128 bit (large) number that represents a unique id for a software application or application component. Typically they are displayed like this "{AE7AB96B-FF5E-4dce-801E-14DF2C4CD681}".

You can think of a CLSID as a "social security number" for a piece of software, or a software component.

What are they used for?CLSIDs are used by Windows to identify software components without having to know their "name". They can also be used by software applications to identify a computer, file or other item.

Where do they come from?Microsoft provides a utility (program) called GUIDGEN.EXE that generates these numbers. They are generated by using the current time, network adapter address (if present) and other items in your computer so that no two numbers will ever be the same.